Unnamed (on Keku Islands)

Prospect, Probably inactive

Commodities and mineralogy

Main commodities W; Zn
Ore minerals pyrite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale PA
Quadrangle map, 1:63,360-scale D-1
Latitude 56.93012
Longitude -134.1347
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is about 1.0 mile south of the center of Payne Island at the northwest end of the unnamed island in section 18, T. 57 S., R. 72 E. The location is accurate.

Geologic setting

Geologic description

This prospect is one of a group of similar deposits (PA021 to PA031) that are scattered along the south shore of Saginaw Bay, on the peninsula north of Saginaw Bay, and on the Keku Islands. They occur in a heterogeneous section of unmetamorphosed volcanic, carbonate, and clastic rocks that vary in age from Silurian to Triassic (Muffler, 1967). The mineralization generally consists of veins, veinlets, and irregular pods that contain base metals and barite (Still and others, 2002). There are no plutonic rocks in the immediate vicinity; however, the sedimentary rocks are cut by scattered gabbro dikes. The origin of the deposits is uncertain although most appear to be epigenetic. Various origins have been proposed including that they are remobilized massive-sulfide deposits, that they are related to a buried intrusive, or that they are Mississippi-Valley-type deposits.
This prospect was first described by Buddington (1925). It was examined by the U.S. Bureau of Mines in 1949 when three claims were active (Jermain and Rutledge, 1949). The host rock of the deposit is the Halleck Formation of Permian age; at this site, it consists of limestone, mudstone and conglomerate (Muffler, 1967). The rocks are cut by a set of Tertiary gabbro dikes that strike 10-50NE and dip 18-20SE. The prospect is associated with one of these dikes (Still and others, 2002). The dike is cut at nearly right angles by a set of sphalerite veinlets 0.1 to 2.0 feet thick that form a system of 'ladder veins', some of which also contain pyrite. Calcite veinlets also crosscut the dikes. Still and others (2002) collected chip samples across several of the veinlets. They contained 7,773 parts per million (ppm) to 13.6 percent zinc and 20 to 149 ppm tungsten. A similar deposit occurs about 0.8 mile to the southeast; chip samples from it contained 6.1 to 31.7 percent zinc and 58 to 254 ppm tungsten.
Geologic map unit (-134.136423790848, 56.929784765109)
Mineral deposit model Sphalerite veinlets.
Age of mineralization The sphalerite veinlets cut Tertiary gabbro dikes.

Production and reserves

Workings or exploration Claims have been staked on the deposit but there is no record of exploration beyond surface sampling.
Indication of production None
Reserve estimates None.

Additional comments

MAS number: 0021160012.


MRDS Number A013381


Reporters Donald J. Grybeck (U.S. Geological Survey)
Last report date 2-Jan-05